The invention relates to a procedure for the continuous production of hoses made of composite materials, such as elastomers and reinforcing inserts, fashioned and heated on a mandrel.
The invention furthermore concerns apparatus for performing this procedure.
The known processes for the manufacture of high pressure hoses from composite materials with an elastic support material can basically be divided into mandrel manufacturing processes and mandrel-less processes.
In mandrel manufacturing processes, the individual material components of the hose, such as the core, the reinforcing insert and the covering, are applied individually to a mandrel of finite length serving as the forming core. The mandrel length is limited for reasons of easy "strippability" and amounts, as a rule, to form 20 to 40 meters. In discontinuous production a solid steel mandrel is usually used for small hose diameters, and an aluminum tube is used for larger diameters on account of greater ease in manipulation (German Pat. No. 521,226).
The mandrel-less processes are the only ones which until now have permitted continuous production of hoses of any desired length, since in this case the limitation of length by the need for ease in removing a mandrel is eliminated. The hose is built up in this case on a slightly compressed fluid, air as a rule. The establishment of the dimensions of the hose is achieved in these processes through the outside diameter, by applying a lead jacket before heating, for example, and removing it continuously again after the heating. In contrast to the mandrel process, the accuracy of the inside diameter in this case depends to a great extent on the material and machine parameters. Furthermore, the mandrel-less processes known today can be used economically only for large hose production and small hose dimensions ("Kautschuk und Gummi" magazine, Feb. 1963, DK 678.06: 621.643.3).
For the manufacture of high pressure hoses, especially those of large and very large dimensions, the mandrel process has heretofore been used exclusively. The reason for this is not so much the required constancy of the inside diameter, but essentially two facts: the metal or textile reinforcement used in making the hose must be fashioned under tension, which in the case of the mandrel-less process, where the inside diameter of the hose is great, would result in an unacceptable constriction of the core. In such cases it is not possible to increase the supporting air pressure, because this would also result in a deformation of the core, but in the opposite sense. On the other hand, jacketing with lead during the heating would result in manufacturing costs which would scarcely be considered reasonable.
Other reasons for the preference of the mandrel processes for the manufacture of high pressure hoses have to do with quality. It is virtually inevitable that, in the fashioning of a hose as a composite material, air will be trapped between the layers of material or the layers will contain some kind of gasifiable components, such as water or solvents, for example, which will be liberated by vulcanization and adversely affect, among other things, the adhesion between the individual layers. To counteract this influence, a high radial pressure is required in the hose cross section during the vulcanization phase, and it matters not whether this application of pressure is accomplished from the inside or the outside, or whether the hose laminations are supported on a pressure resistant outer jacket or on a pressure resistant internal mandrel. However, under identical radial pressure conditions the wall thicknesses of the supporting bodies differ greatly.
Thus, in the case of a hose with an inside diameter of 100 mm and an outside diameter of 120 mm, the wall thickness of an outer supporting jacket must be 4 times greater than that of an internal hollow mandrel in order to produce the same compression of the layers in the hose cross section and thus equal quality in the product. The comparable amount of the "mandrel material" that is used is even smaller by a factor of 7 in the case of external application of pressure.
In addition to this disadvantageous circumstance for the pressure jacket process, the limitation of the absolute internal pressure for the reasons described is a handicap which does not affect the mandrel process.